Think of your tendons as a cable on a winch. When the cable gets frayed from over-use the cable weakens. Two weeks of using only low sets/high reps will help repair the frays in the tendons from the heavy-higher volume lifting done during the 6 week mass phase. Those who neglect the 2 week prime eventually move backwards because of nagging injuries. It's comparable to those who neglect to repair the cable on their winches when they begin to fray. Remember, you cannot see tendon damage occuring or go buy a new set of tendons at the local Wamart like you can a cable for a winch when it goes bad! I cannot stress enough how important it is to perform a 2 week prime after 6 weeks of heavy-higher volume lifting.